Safety systems are used in a many different environments ranging from personal safety systems to wide-reaching, networked safety systems. Small scale safety systems include, for example, home security systems, smoke detectors, and the like. On a larger scale, buildings and campuses generally include safety and possibly security systems. For example, fire and smoke systems, access systems, security systems, etc. are all within the purview of building safety systems. Due to the size of buildings relative to single-family dwellings and the generally higher number of people that may be within the building at a given time, additional safety requirements are usually necessary. These additional safety requirements are driven by the desire to provide a safe and functional environment, and may also be driven by various safety regulations. Agencies such as the National Fire Protection Association (NFPA), Occupational Safety & Health Administration, etc. set forth requirements for certain safety systems, particularly fire safety systems. In addition to these regulatory requirements, certification of various aspects of a system may be obtained from other organizations, such as the Underwriters Laboratories Inc. (UL).
Specific components or devices used in fire safety systems may be individually UL-approved. For example, smoke detectors, heat sensors, alarm pull stations and other devices that form part of the collective fire alarm system may require UL approval. Vendors of such individual components may obtain the requisite UL approval. However, a system developer may be subject to system-level safety requirements, such as the interface between such components, control of the components, component redundancies, communication link redundancies, etc. In these cases, the system developer often seeks UL approval at the system level.
Today's networking technologies provide the system developer with great flexibility in monitoring and controlling fire systems. For example, monitoring and/or control of discrete detectors or groups of detectors may be accomplished at a central location, or such functions may be distributed over multiple locations. Monitoring and control may be performed through direct communication links, through Local Area Networks (LANs), and/or remotely. To facilitate aggregate monitoring and control of the various detectors and components used in the fire system, these detectors and components may be networked with a central processing system(s). In some cases, direct communication links may be sufficient, such as where a small number of detectors are utilized, and a central processing system can directly monitor and control such devices. At the other end of the spectrum, fire systems can be monitored and controlled via Wide Area Networks (WANs) or Global Area Networks (GANs) such as the Internet, where one or more central processing systems monitor and control devices at remote locations. A common implementation is a fire system located within a building or campus, where LANs are used to facilitate communication between the processing systems and the sensors, detectors, etc. System-level safety requirements may dictate the manner in which such systems operate via the LAN or other network. One such system-level requirement involves the integrity of communication links within the network environment of a fire safety system.
In the context of LANs, for example, various communication protocols and physical media may be used. For example, LANs may be established using different types of physical links, such as twisted-pair wires, coaxial cable, etc. Different communication protocols may be used to communicate over the physical links. As a particular example, one commonly implemented LAN implementation employs Ethernet technology. Ethernet technology and its analogous Institute of Electrical and Electronics Engineers, Inc. (IEEE) 802.3 standards are well known local area networking technologies. As previously indicated, system-level safety requirements may govern the manner in which LAN connections, such as Ethernet connections, are to be implemented in order to comply with safety regulations. For example, a requirement exists in some fire system applications that redundant communication paths be provided to monitor the integrity of the communication links associated with the LAN connection. One example of such a requirement is UL standard 864, which is a standard for control units for fire-protective signaling systems. This standard is based upon NFPA 72, the National Fire Alarm Code. This code explicitly describes the current requirements for redundant communication paths used in safety systems. Presently, there is no system that complies with this code for fire safety systems using redundant Ethernet (or analogous) LAN connections.
Accordingly, there is a need for a manner of providing reliable, redundant network communication links in safety systems such as fire safety systems. The present invention fulfills these and other needs, and offers other advantages over the prior art.